Personally, I feel that since you’re offering it from one domain and it’s intended to be a new feature to an existing site, it should fall under one license… Even though, in the statement previously made he declared the need for a separate license for a “sub-domain” or “sub folder”. That being said though, technically, it is no longer a “single installation” even though it acts as one… and confirming with Bastian would probably be the best approach.